Temperature sensing return electrode pad

ABSTRACT

An electrosurgical return electrode is disclosed. The return electrode includes a conductive pad having one or more temperature monitoring zones and a patient-contacting surface configured to conduct electrosurgical energy and a temperature sensing circuit coupled to the conductive pad. The temperature sensing circuit includes at least one diode disposed within the at least one temperature monitoring zone, the at least one diode having a predetermined forward voltage drop that is indicative of temperature of at least one temperature monitoring zone.

BACKGROUND

1. Technical Field

The present disclosure relates to electrosurgical apparatuses, systemsand methods. More particularly, the present disclosure is directed tomonopolar electrosurgical systems utilizing one or more return electrodepads configured to sense temperature.

2. Background of Related Art

Energy-based tissue treatment is well known in the art. Various types ofenergy (e.g., electrical, ultrasonic, microwave, cryo, heat, laser,etc.) may be applied to tissue to achieve a desired surgical result.Electrosurgery typically involves application of high radio frequencyelectrical current to a surgical site to cut, ablate, coagulate or sealtissue. In monopolar electrosurgery, a source or active electrodedelivers radio frequency energy from the electrosurgical generator tothe tissue and a return electrode carries the current back to thegenerator. In monopolar electrosurgery, the source electrode istypically part of the surgical instrument held by the user and appliedto the tissue to be treated. The patient return electrodes are typicallyin the form of pads adhesively adhered to the patient and are placedremotely from the active electrode to carry the current back to thegenerator.

The return electrodes usually have a large patient contact surface areato minimize heating at that site since the smaller the surface area, thegreater the current density and the greater the intensity of the heat.That is, the area of the return electrode that is adhered to the patientis important because it is the current density of the electrical signalthat heats the tissue. A larger surface contact area is desirable toreduce localized heat intensity. Return electrodes are typically sizedbased on assumptions of the maximum current utilized during a particularsurgical procedure and the duty cycle (i.e., the percentage of time thegenerator is on).

The first types of return electrodes were in the form of large metalplates covered with conductive jelly. Later, adhesive electrodes weredeveloped with a single metal foil covered with conductive jelly orconductive adhesive. However, one problem with these adhesive electrodeswas that if a portion peeled from the patient, the contact area of theelectrode with the patient decreased, thereby increasing the currentdensity at the adhered portion and, in turn, increasing the heat appliedto the tissue. This risked burning the patient in the area under theadhered portion of the return electrode if the tissue was heated beyondthe point where circulation of blood could cool the skin.

To address this problem various return electrodes and hardware circuits,generically called Return Electrode Contact Quality Monitors (RECQMs),were developed. Such systems relied on measuring impedance at the returnelectrode to calculate a variety of tissue and/or electrode properties(e.g., degree of electrode adhesiveness, temperature). These systemswere only configured to measure temperature as a function of the changesin impedance of the return electrode pads.

SUMMARY

The present disclosure relates to an electrosurgical return electrodethat includes a conductive pad having a patient-contacting surface. Theconductive pad includes a temperature circuit coupled to a power sourceand electrically insulated from the patient-contacting surface. Thetemperature circuit includes one or more diodes coupled in series withone or more resistors. The diodes are located within predeterminedtemperature measuring zone and provide for temperature measurementwithin corresponding temperature monitoring zones. In particular, theforward bias voltage across the diodes varies with the temperature.Thus, by monitoring the voltage, temperature can be monitored as afunction thereof.

According to one aspect of the present disclosure, an electrosurgicalreturn electrode is provided. The return electrode includes a conductivepad having one or more temperature monitoring zones and apatient-contacting surface configured to conduct electrosurgical energyand a temperature sensing circuit operatively associated with theconductive pad. The temperature sensing circuit includes at least onediode disposed within the at least one temperature monitoring zone, theat least one diode having a predetermined forward voltage drop which isindicative of temperature of at least one temperature monitoring zone.

A method for performing electrosurgery is also contemplated by thepresent disclosure. The method includes the steps of providing anelectrosurgical return electrode including a conductive pad having oneor more temperature monitoring zones and a patient-contacting surfaceconfigured to conduct electrosurgical energy and a temperature sensingcircuit operatively associated with the conductive pad. The temperaturesensing circuit includes at least one diode disposed within the at leastone temperature monitoring zone, the at least one diode having apredetermined forward voltage drop which is indicative of temperature ofat least one temperature monitoring zone. The method also includes thesteps of placing the electrosurgical return electrode in contact with apatient, generating electrosurgical energy via an electrosurgicalgenerator, supplying the electrosurgical energy to the patient via anactive electrode, and monitoring the predetermined forward voltage dropto measure the temperature of the at least one temperature monitoringzone.

According to another aspect of the present disclosure an electrosurgicalsystem for performing electrosurgery is disclosed. The electrosurgicalsystem includes an electrosurgical generator configured to provideelectrosurgical energy and an electrosurgical return electrode. Thereturn electrode includes a conductive pad having one or moretemperature monitoring zones and a patient-contacting surface configuredto conduct electrosurgical energy and a temperature sensing circuitoperatively associated with the conductive pad. The temperature sensingcircuit includes at least one diode disposed within the at least onetemperature monitoring zone, the at least one diode having apredetermined forward voltage drop which is indicative of temperature ofat least one temperature monitoring zone. The system also includes anactive electrode to supply electrosurgical energy to a patient.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a schematic block diagram of an electrosurgical systemaccording to the present disclosure;

FIG. 2 is a schematic block diagram of a generator according to oneembodiment of the present disclosure;

FIG. 3 is a top view of the electrosurgical return electrode of themonopolar electrosurgical system of FIG. 1;

FIG. 4 is a cross-sectional side view of an electrosurgical returnelectrode having a positive temperature coefficient (PTC) material andadhesive material layers;

FIGS. 5A-B illustrate one embodiment of an electrosurgical returnelectrode having temperature sensing circuit according to the presentdisclosure; and

FIG. 6 is a cross-sectional plan view of another embodiment of anelectrosurgical return electrode having temperature sensing circuitaccording to the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail.

FIG. 1 is a schematic illustration of an electrosurgical systemaccording to one embodiment of the present disclosure. The systemincludes an electrosurgical instrument 2 having one or more electrodesfor treating tissue of a patient P. The instrument 2 is a monopolarinstrument including one or more active electrodes (e.g.,electrosurgical cutting probe, ablation electrode(s), etc.).Electrosurgical RF energy is supplied to the instrument 2 by a generator20 via an electrosurgical cable 4, which is connected to an activeoutput terminal, allowing the instrument 2 to coagulate, seal, ablateand/or otherwise treat tissue. The energy is returned to the generator20 through a return electrode 6 via a return cable 8. The system mayinclude a plurality of return electrodes 6 that are arranged to minimizethe chances of tissue damage by maximizing the overall contact area withthe patient P. In addition, the generator 20 and the return electrode 6may be configured for monitoring so-called “tissue-to-patient” contactto insure that sufficient contact exists therebetween to furtherminimize chances of tissue damage.

The generator 20 includes input controls (e.g., buttons, activators,switches, touch screen, etc.) for controlling the generator 20. Inaddition, the generator 20 may include one or more display screens forproviding the user with variety of output information (e.g., intensitysettings, treatment complete indicators, etc.). The controls allow theuser to adjust power of the RF energy, waveform, and other parameters toachieve the desired waveform suitable for a particular task (e.g.,coagulating, tissue sealing, intensity setting, etc.). The instrument 2may also include a plurality of input controls that may be redundantwith certain input controls of the generator 20. Placing the inputcontrols at the instrument 2 allows for easier and faster modificationof RF energy parameters during the surgical procedure without requiringinteraction with the generator 20.

FIG. 2 shows a schematic block diagram of the generator 20 having acontroller 24, a high voltage DC power supply 27 (“HVPS”) and an RFoutput stage 28. The HVPS 27 provides high voltage DC power to an RFoutput stage 28, which then converts high voltage DC power into RFenergy and delivers the RF energy to the active electrode. Inparticular, the RF output stage 28 generates sinusoidal waveforms ofhigh RF energy. The RF output stage 28 is configured to generate aplurality of waveforms having various duty cycles, peak voltages, crestfactors, and other suitable parameters. Certain types of waveforms aresuitable for specific electrosurgical modes. For instance, the RF outputstage 28 generates a 100% duty cycle sinusoidal waveform in cut mode,which is best suited for ablating, fusing and dissecting tissue, and a1-25% duty cycle waveform in coagulation mode, which is best used forcauterizing tissue to stop bleeding.

The controller 24 includes a microprocessor 25 operably connected to amemory 26, which may be volatile type memory (e.g., RAM) and/ornon-volatile type memory (e.g., flash media, disk media, etc.). Themicroprocessor 25 includes an output port that is operably connected tothe HVPS 27 and/or RF output stage 28 allowing the microprocessor 25 tocontrol the output of the generator 20 according to either open and/orclosed control loop schemes. Those skilled in the art will appreciatethat the microprocessor 25 may be substituted by any logic processor(e.g., control circuit) adapted to perform the calculations discussedherein.

A closed loop control scheme is a feedback control loop wherein sensorcircuit 22, which may include a plurality of sensors measuring a varietyof tissue and energy properties (e.g., tissue impedance, tissuetemperature, output current and/or voltage, etc.), provides feedback tothe controller 24. Such sensors are within the purview of those skilledin the art. The controller 24 then signals the HVPS 27 and/or RF outputstage 28, which then adjust DC and/or RF power supply, respectively. Thecontroller 24 also receives input signals from the input controls of thegenerator 20 or the instrument 2. The controller 24 utilizes the inputsignals to adjust power outputted by the generator 20 and/or performsother control functions thereon.

FIGS. 3 and 4 illustrate various embodiments of the return electrode 6for use in monopolar electrosurgery. The return electrode 6 includes aconductive pad 30 having a top surface and a patient-contacting surface32 configured to receive current during monopolar electrosurgery. Thepatient-contacting surface 32 is made from a suitable conductivematerial such as metallic foil. While FIG. 3 depicts the returnelectrode 6 in a general rectangular shape, it is within the scope ofthe disclosure for the return electrode 6 to have any suitable regularor irregular shape.

Referring to FIG. 4, another embodiment of the return electrode 6 isshown, wherein the conductive pad 30 includes a positive temperaturecoefficient (PTC) material layer 38 deposited thereon. The PTC material38 can be made of, inter alia, a polymer/carbon-based material, acermet-based material, a polymer material, a ceramic material, adielectric material, or any combinations thereof. The PTC material layer38 acts to distribute the temperature created by the current over thesurface of the electrosurgical return electrode 6, which minimizes therisk of a patient burn. The return electrode 6 further includes anadhesive material layer 39 on the patient-contacting surface 32. Theadhesive material can be, but is not limited to, a polyhesive adhesive,a Z-axis adhesive, a water-insoluble, hydrophilic, pressure-sensitiveadhesive, or any combinations thereof, such as POLYHESIVE™ adhesivemanufactured by Valleylab of Boulder, Colo. The adhesive material layer39 ensures an optimal surface contact area between the electrosurgicalreturn electrode 6 and the patient “P,” which limits the possibility ofa patient burn. In an embodiment where PTC material layer 38 is notutilized, the adhesive material layer 39 may be deposited directly ontothe patient-contacting surface 32.

FIGS. 5A and 5B shows the return electrode 6 including a temperaturesensing circuit 40 disposed therein. The temperature sensing circuit 40includes one or more temperature sensor arrays 41 and 43 having at leastone temperature sensor. Contemplated temperature sensors includethermocouples, thermistors, semiconductor (e.g., silicon) diodes,ferrite materials and Hall effect devices. The temperature sensingcircuit 40 is disposed on a flex circuit (e.g., a flexible holdingsubstrate 48) manufactured from suitable substrate, such as a polyimidefilm. Examples are films sold under the trademarks MYLAR™ and KAPTON™and the like.

The diodes 42 are connected in series with one or more current limitingresistors 44 and are utilized as temperature sensors. The resistor 44 iscoupled in series with the diode 42, having a resistance selected to setand limit the current flowing through the diode 42 at a predeterminedlevel. The current flow to the diodes 42 is provided by a power source50, such as a low voltage DC power source (e.g., battery, AC/DCtransformer, etc.) connected in series with the diodes 42 and resistors44 via interconnection wires 46. The power source 50 may be integratedinto the generator 20 and draw power from the same source as the HVPS 27(e.g., AC outlet). In one embodiment, interconnection of the diodes 42and the resistors 44 is achieved by deposition of metal traces on theholding substrate 48 and soldering of the diodes 42 and the resistors 44directly into the holding substrate 48. The holding substrate 48 mayalso electrically insulate the temperature sensing circuit 40 from thepatient-contacting surface 32 to prevent RF energy being returned to thegenerator 20 from interfering with the circuit components.

The diodes 42 are forward biased such that current flows initiallythrough the resistor 44 and from the diode's anode to the diode'scathode. In a forward biased diode 42, forward voltage drop (Vf) isproduced that is in the range of about 0.5V to about 5V depending on thetype of diode (e.g., light emitting diode). The forward voltage isdirectly dependent on the temperature. In particular, as the temperatureincreases, the semiconductor material within the diode 42 undergoeschanges in their valence and conduction bands and consequently Vfdecreases. Thus, by keeping the current flowing through the diode 42constant via the resistor 44 and measuring the forward bias voltageallows for determination of the temperature of the diode 42.

The Vf signal is transmitted through the interconnection wires 46 to thegenerator 20, wherein the sensor circuit 22 analyzes the Vf to determinea corresponding temperature value. As those skilled in the art willappreciate, each of the interconnection wires 46 may include acorresponding isolation circuit (e.g., optical couplers) to translateelectric signals (e.g., Vf) across isolation barriers, thereby isolatingthe temperature sensing circuit 40 from the RF supply.

The analysis process may include passing the Vf signals through ananalog-to-digital converter and then multiplying the digitized Vf signalby a predetermined factor to arrive at a corresponding temperaturevalue. The factor is derived empirically taking into considerationelectrical properties of the diode 42, resistor 44 as well as electricalproperties of the current being passed therethrough. The temperaturesignal is then transmitted to the controller 24 where it is furtheranalyzed to determine appropriate action. For instance, comparingtemperature measurements with a predetermined temperature threshold andadjusting or terminating the RF energy supply if the temperaturemeasurement is larger than the predetermined threshold.

Temperature across the patient-contacting surface 32 may vary due to anumber of factors (e.g., moisture content, adherence, etc.) affectingcurrent density. Therefore, it may be desirable to measure temperaturesat various points in the conductive pad 30. Measuring temperature atvarious points allows for pinpointing the location of so-called “hotspots,” segments of the patient-contacting surface 32 where currentdensity exceeds that of the surrounding area and results in pad burn.Since measurement of Vf for each diode 42 provides for determination ofcorresponding temperature at the location of the diode 42, placing thediodes 42 strategically within the conductive pad 30 allows formonitoring of temperature at those locations.

With reference to FIG. 5A, each resistor 44 and diode 42 pair isdisposed within the conducting pad 30 such that the diode 42 providestemperature readings for a corresponding temperature monitoring zone 45.The size of the monitoring zone 45 depends on the distance between thediodes 42. The conductive pad 30 may include any number of monitoringzones 45 of varying sizes. Each diode 42 is identified by the sensorcircuit 22 as being associated with a particular monitoring zone 45 suchthat, when Vf signals are transmitted and subsequently converted intotemperature readings, the generator 20 provides temperature monitoringfor each of the monitoring zones 45. This data is utilized to instructthe user which specific portion of the conductive pad 30 includes a hotspot so that preventative action may be taken, if necessary. This mayinclude automatic RF supply termination and/or adjustment or manualtermination of RF supply to ensure that the conductive pad 30 adheresproperly to the patient at the identified hot spot.

As shown in FIG. 6, the temperature sensor arrays 41 and 43 include asingle resistor 44 connected in series with a plurality of diodes 42disposed within a respective temperature monitoring zone 45. Since thediodes 42 are connected in series to one resistor 44, the currentsupplied to the diodes 42 is the same. Consequently, measuring the Vfacross the diodes 42 provides the temperature for the entire respectivetemperature monitoring zone 45. This circuit arrangement provides anaverage temperature measurement over larger segments of the conductivepad 30 (e.g., entire area). Those skilled in the art will appreciatethat various configurations of the resistor 44 and diode 42 arecontemplated to ensure that temperature of various segments of theconductive pads 30 are monitored.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

1. An electrosurgical return electrode, comprising: a conductive padincluding at least one temperature monitoring zone and apatient-contacting surface configured to conduct electrosurgical energy;and a temperature sensing circuit coupled to the conductive pad, thetemperature sensing circuit including at least one diode disposed withinthe at least one temperature monitoring zone, the at least one diodehaving a predetermined forward voltage drop that is indicative oftemperature of the at least one temperature monitoring zone.
 2. Anelectrosurgical return electrode according to claim 1, wherein the atleast one diode is forward biased.
 3. An electrosurgical returnelectrode according to claim 1, further comprising a holding substratefor housing the temperature sensing circuit, the holding substrate beingconfigured to electrically insulate the temperature sensing circuit fromthe patient-contacting surface.
 4. An electrosurgical return electrodeaccording to claim 1, wherein the temperature sensing circuit includesat least one resistor coupled in series with the at least one diode. 5.An electrosurgical return electrode according to claim 4, wherein thetemperature sensing circuit is coupled to at least one power sourceconfigured to supply current to the at least one diode.
 6. Anelectrosurgical return electrode according to claim 5, wherein the atleast one resistor is configured to limit the current flowing throughthe at least one diode to a predetermined level.
 7. The electrosurgicalreturn electrode according to claim 1, wherein the conductive padincludes an adhesive material disposed on the patient-contactingsurface.
 8. The electrosurgical return electrode according to claim 1,wherein the conductive pad is at least partially coated with a positivetemperature coefficient (PTC) material.
 9. A method for performingelectrosurgery, comprising: providing an electrosurgical returnelectrode having a conductive pad that includes at least one temperaturemonitoring zone and a patient-contacting surface configured to conductelectrosurgical energy, and a temperature sensing circuit coupled to theconductive pad, the temperature sensing circuit including at least onediode disposed within the at least one temperature monitoring zone, theat least one diode having a predetermined forward voltage drop that isindicative of temperature of the at least one temperature monitoringzone; placing the electrosurgical return electrode in contact with apatient; generating electrosurgical energy from an electrical energysource; supplying the electrosurgical energy to the patient via anactive electrode; and monitoring the predetermined forward voltage dropto measure the temperature of the at least one temperature monitoringzone.
 10. A method according to claim 9, wherein the at least one diodeis forward biased.
 11. A method according to claim 9, further comprisinga holding substrate for housing the temperature circuit, the holdingsubstrate being configured to electrically insulate the temperaturesensing circuit from the patient-contacting surface.
 12. A methodaccording to claim 9, wherein the temperature sensing circuit includesat least one resistor coupled in series with the at least one diode. 13.A method according to claim 12, further comprising the step of:supplying current to the at least one diode.
 14. A method according toclaim 13, further comprising the step of: limiting the current flowingthrough the at least one diode to a predetermined level.
 15. Anelectrosurgical system for performing electrosurgery, theelectrosurgical system comprising: an electrosurgical generatorconfigured to provide electrosurgical energy; an electrosurgical returnelectrode including a conductive pad including at least one temperaturemonitoring zone and a patient-contacting surface configured to conductelectrosurgical energy, and a temperature sensing circuit operativelyassociated with the conductive pad, the temperature sensing circuitincluding at least one diode disposed within the at least onetemperature monitoring zone and at least one resistor coupled in serieswith the at least one diode, the at least one diode having apredetermined forward voltage drop that is indicative of temperature ofthe at least one temperature monitoring zone; and an active electrode tosupply electrosurgical energy to a patient.
 16. An electrosurgicalsystem according to claim 15, wherein the at least one diode is forwardbiased.
 17. An electrosurgical system according to claim 15, furthercomprising a holding substrate for housing the temperature sensingcircuit, the holding substrate being configured to electrically insulatethe temperature sensing circuit from the patient-contacting surface. 18.An electrosurgical system according to claim 15, wherein the temperaturesensing circuit is coupled to at least one power source configured tosupply current to the at least one diode.
 19. An electrosurgical systemaccording to claim 18, wherein the at least one resistor is configuredto limit the current flowing through the at least one diode to apredetermined level.